Researchers followed nearly 800 U.S. firefighters, asking how closely they followed a Mediterranean-style diet. They gathered information about weight changes over the previous five years, and collected data on cholesterol, blood pressure and blood sugar levels.

They compared the firefighters who followed a Mediterranean-style diet the closest with those who followed it the least closely, separating the men into four groups.

The more closely the men stuck to the diet, the lower their risk of developing some key markers for potential heart trouble, said Dr. Stefanos Kales, an associate professor of medicine at Harvard Medical School and Harvard School of Public Health.

Those who adhered most strongly to the diet had a 35 percent lower risk of being diagnosed with metabolic syndrome compared to the group that adhered the least. Metabolic syndrome is a group of factors that increases the risk of heart disease, stroke and diabetes. Those risk factors include having a large waist, high levels of triglycerides, low levels of "good" cholesterol, high blood pressure and high blood sugar levels.

Those who adhered most closely to the Mediterranean diet also had a 43 percent lower risk of weight gain compared to those who adhered the least closely.

The study was published online Feb. 4 in the journal PLoS One.

Those who adhered most closely to the diet, Kales said, "tended not to drink soft drinks or other sugary beverages; had less consumption of fast food and more fruits and vegetables; ate fewer sweets; and were less likely to eat fried food."

If people want to pick just a couple things to change, he said, avoiding fast food and sugary drinks would be key targets.

In study after study, the researchers said, the Mediterranean diet has been linked with better health status.

The researchers studied firefighters partly because they are known to have a high prevalence of obesity and risk factors for heart disease, Kales said.

Connie Diekman, director of university nutrition at Washington University in St. Louis, said the findings make sense and are not surprising.

"This study is one more in the long line of Mediterranean diet studies showing the benefit of a lifestyle that encompasses more plant foods and regular activity," said Diekman, author of The Everything Mediterranean Diet Book.

Among the study's limitations, acknowledged by the researchers, is that the questionnaire about diet was developed to obtain general diet information, so the researchers didn't have data on total energy intake and certain traditional Mediterranean food groups such as nuts and legumes.

Diekman said, however, that the study "does provide support to the benefit of limiting high-fat and high-sugar foods by using more plant foods."

"[The study] complements the already large number of studies that show why a plant-based diet with leaner, lower fat protein choices and regular activity is better for health," she said.